Through over-use, traumatic events and/or debilitating disease, a person's joint may become damaged to the point that the joint is repaired. One type of procedure to address damage to a person's joint is an arthroplasty procedure. Arthroplasty is a medical procedure where a joint of a patient is replaced, remodeled, or realigned, often done to relieve pain in the joint after damage. Damage to the joint may result in a reduction or wearing away of cartilage in the joint area, which operates to provide frictional, compressive, shear, and tensile cushioning within the joint. As such, reduction in cartilage in a joint causes pain and decreased mobility of the joint. To combat this joint pain, a patient may undergo the arthroplasty procedure to restore function and use back to the damaged joint.
One type of arthroplasty procedure is known as Total Knee Arthroplasty (TKA). In general, TKA involves replacing the diseased or damaged portion of the knee with metal or plastic components that are shaped to approximate the shape of the replaced portion or shaped to allow movement of the joint and relieve the joint pain. Thus, a TKA procedure may include replacement of a portion of the femur and a portion of the tibia that make up the knee joint. Similar procedures may be performed on other damaged joints, such as a hip, a shoulder, an elbow, and the like. General discussion of arthroplasty procedures herein are directed specifically to TKA-type procedures, but may be applied to arthroplasty procedures of other types of joints.
In a TKA procedure, a damaged portion of the distal region of the femur is removed and replaced with a metal or plastic component that is shaped to mirror or approximate the replaced portion. The metal or plastic component may be impacted onto the femur or fixed using a type of surgical cement or other fastening system. Further, a proximal portion of the tibia may also be removed and replaced with a generally flat metal or plastic component that is shaped to mirror or approximate the replaced portion. The tibia replacement implant may also be attached to the tibia through impaction onto the bone or fixed using a type of cement. In general, the femur implant and the tibia implant are mated to form a joint that approximates the shape and operation of the knee joint. In some examples, a plastic surface is placed between the femur implant and the tibia implant to prevent metal-on-metal interaction between the implants during use of the replaced joint.
As mentioned above, a TKA procedure often involves the removal and replacement of portions of the femur and/or tibia of the injured knee. During the removal, the portions of the femur and tibia may be cut, drilled, resurfaced, and the like to create a surface on the bones that mates with the respective implants. In one particular example, the ends of the bones (distal end of the femur and proximate end of the tibia) may be completely removed to create a generally flat surface to which the implants are mated. Once the mating surfaces for the implants are created on the receiving bones, the implants may then be attached to the bones as described above.
Although the broad outline of the TKA procedures is described above, there is much to consider when performing the procedure. For example, patients may undergo a preoperative planning phase of the procedure through one or more consultations with a doctor that could last a month or more before the TKA is performed. In addition, alignment of the implants in the joint with the rest of the patient's anatomy is crucial to the longevity of the implant and the implant's effectiveness in counteracting the pre-TKA joint condition. As such, systems and methods have been developed to produce customized arthroplasty cutting jigs that allow a surgeon to quickly and accurately perform the necessary resections of the bones that result in a successful TKA procedure. In particular, cutting jigs may be generally customized for the particular patient's joint undergoing the TKA procedure to ensure that the implants align with the patient's anatomy post-procedure. Through the use of such customized cutting jigs, the TKA procedure is both more accurate (ensuring more longevity to the implants) and quicker (reducing the time required for the surgical procedure, thereby reducing the potential for post-surgery complications).
In general, cutting guides or cutting jigs used in TKA procedures may attach to one or more bones of the knee and provide a cut line to the surgeon for use during the TKA surgery. In particular, a femur cutting jig may attach to the distal end of the femur and include a cut guide or line. A surgeon, during the procedure, inserts a saw device into or through the cut line to resect the distal end of the femur. Similarly, a tibia cutting jig may attach to the proximal end of the tibia and include a cut line that the surgeon uses to resect the proximal end of the tibia. In this manner, the ends of the femur and tibia are resected by the surgeon during the TKA procedure, thereby creating a smooth mating surface for the implants.
The cutting jigs used in the TKA procedure may attach to the bones of the knee in various ways. General cutting jigs (cutting jigs that do not incorporate customization to the particular patient's anatomy) may attach to the femur and tibia to provide the resection line for the surgeon. Such general cutting jigs often require the surgeon to align the cut line into the proper position during attachment of the cutting jig. As can be appreciated, such general cutting jigs result in vastly different quality of effectiveness, mostly based on the experience and skill of the surgeon. Customized cutting jigs, on the other hand, are designed to mate with the particular patient's femur and/or tibia to reduce the amount of incorrect attachment of the cutting jig to the patient's knee. Through the use of customized cutting jigs, surgeon error in TKA procedures may be greatly reduced.
The customization of the arthroplasty cutting jigs may vary from procedure to procedure. In one simple example, the customization may include merely selecting one jig from a group of generalized cutting jigs of various sizes in an attempt to match the size of the patient's anatomy. On the other end of the spectrum, the customized arthroplasty cutting jig may provide a mating surface that is the exact negative of the femur or tibia for attachment to the bone surface. Regardless of the customization of the cutting jig used, the jig should be designed to provide the proper location and orientation on the bones of the affected joint such that treatment of the region can be performed accurately, safely, and quickly.
Images of orthopedic joints that are candidates for partial or total replacement are often formed as MRI images, referred to here as “slices,” with each such image being a projection on a two dimensional image forming substrate. Each such MRI image is actually a three dimensional “voxel,” representing a thickness of approximately 2 mm of partial images of cortical bone, cancellous bone cartilage and open space, with each such material having its own range of grey scales in the MRI image. For a full three dimensional representation of an anatomical surface AS of interest, it is often necessary to provide tens to hundreds of MRI slices in two or more of three views (coronal or front view, axial or top view, and sagittal or side view) for a given anatomical component.
Many of the knee replacement procedures presently use what is characterized as “full segmentation” in order to represent a relevant portion of a femur or a tibia surface in three dimensions. This approach requires use of a dense, three dimensional grid of points to accurately represent a surface, especially a surface having cusps or sharp corners with very small associated radii of curvature. This approach has several disadvantages, including the following: (1) this approach is time consuming, often requiring 4-20 hours of intense numerical work to generate and check the accuracy of the grid point coordinates for a single surface; (2) because of the time required to implement this approach for a single surface, use of this approach in mass manufacturing of custom or semi-custom instruments is limited; (3) this approach may introduce geometrical errors, including closing errors; (4) because of the close spacing of grid points, polynomials of high mathematical degree are be used, which can introduce undesirable “ripples” in the mathematical surface produced by a full segmentation process; and (5) formation and analysis of a large number of MRI slices is required
It is with these and other issues in mind that various aspects of the present disclosure were developed.